WO2013122436A1

WO2013122436A1 - Apparatus and method for transmitting/receiving reference signal in cellular radio communication system using cooperative multi-point scheme

Info

Publication number: WO2013122436A1
Application number: PCT/KR2013/001250
Authority: WO
Inventors: Hyo-Jin Lee; Youn-Sun Kim; Ki-Il Kim; Ju-Ho Lee; Joon-Young Cho; Hyoung-Ju Ji
Original assignee: Samsung Electronics Co., Ltd.
Priority date: 2012-02-17
Filing date: 2013-02-18
Publication date: 2013-08-22
Also published as: KR20130095232A; KR102126990B1

Abstract

Provided is a method for transmitting a DeModulation Reference Signal (DMRS) by a Node B in a cellular radio communication system using a Cooperative Multi-Point (CoMP) scheme. The method includes transmitting a DMRS based on a preset DMRS scrambling sequence, for at least one antenna port, wherein the DMRS scrambling sequence is initialized with an initial value at a start of each sub-frame, and wherein the initial value is determined using an identifier of the DMRS scrambling sequence, a slot number of a serving (or primary) cell of a related User Equipment (UE), a sub-frame offset value based on the DMRS scrambling sequence, and a parameter related to a cell identifier of a cell for which the related UE has reported a Reference Signal Received Power (RSRP) at least once.

Description

APPARATUS AND METHOD FOR TRANSMITTING/RECEIVING

REFERENCE SIGNAL IN CELLULAR RADIO COMMUNICATION SYSTEM USING COOPERATIVE MULTI-POINT SCHEME

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for transmitting/receiving a Reference Signal (RS) in a cellular radio communication system. More particularly, the present invention relates to an apparatus and method for transmitting/receiving a DeModulation Reference Signal (DMRS) in a Cooperative Multi-Point (CoMP) cellular radio communication system in which a plurality of Node Bs provide a User Equipment (UE) with a service using a CoMP scheme.

2. Description of the Art

A communication system supports a DownLink (DL) communication that conveys signals from one or more Transmission Points (TPs) to UEs, and a UpLink (UL) communication that conveys signals from UEs to one or more Reception Points (RPs). A UE, also commonly referred to as a terminal or a Mobile Station (MS), may be fixed or mobile and may be a wireless device, a cellular phone, a personal computer device, etc. A TP or a RP is generally a fixed station and may also be referred to as a Base Transceiver System (BTS), a Node B, an enhanced Node B (eNB), an access point, etc.

A communication system also supports the transmission of several signal types for its proper functionality including data signals conveying information content, control signals enabling proper processing of data signals, and Reference Signals (RSs), also known as pilots, enabling coherent demodulation of data or control signals or providing Channel State Information (CSI) corresponding to an estimate of the channel medium experienced by their transmission.

UL data information is conveyed through a Physical UL Shared CHannel (PUSCH). UL Control Information (UCI) is conveyed through a Physical UL Control CHannel (PUCCH) unless a UE also has a PUSCH transmission in which case the UE may convey at least some UCIs together with data information through the PUSCH. The UCI includes ACKnowledgment (ACK) information associated with the use of a Hybrid Automatic Repeat reQuest (HARQ) process as HARQ-ACK information.

The HARQ-ACK information indicates that a UE has normally received a signal transmitted from a Node B to the UE, e.g., Transport Blocks (TBs) transmitted from the Node B to the UE in a DL of the communication system. The DL TBs are transmitted through a Physical Downlink Shared CHannel (PDSCH). The UCI may also include a Channel Quality Indicator (CQI), or a Precoding Matrix Indicator (PMI), or a Rank Indicator (RI), which may be jointly referred to as Channel State Information (CSI).

The CQI provides to the Node B a measure of the Signal to Interference and Noise Ratio (SINR) the UE experiences over sub-bands or over the whole operating DL Bandwidth (BW). The SINR measure is typically in the form of the highest level-Modulation and Coding Scheme (MCS) for which a predetermined BLock Error Rate (BLER) can be achieved for the transmission of TBs.

The PMI/RI informs the Node B how to combine the signal transmission to the UE from multiple Node B antennas in accordance with the Multiple-Input Multiple-Output (MIMO) scheme. The UE may transmit the UCI either separately from data information in a Physical Uplink Control CHannel (PUCCH) or together with data information through a Physical Uplink Shared CHannel (PUSCH).

DL data information is conveyed through a Physical DL Shared CHannel (PDSCH). DL Control Information (DCI) includes DL CSI feedback request to UEs, Scheduling Assignments (SAs) for PUSCH transmissions from UEs (UL SAs) or for PDSCH receptions by UEs (DL SAs). The SAs are conveyed through DCI formats transmitted in respective Physical DL Control CHannels (PDCCHs). In addition to the SAs, PDCCHs may convey DCI that is commonly applied to all UEs or to a group of UEs.

The DCI also includes HARQ-ACK information that one or more TPs transmit to UEs through Physical HARQ-ACK Indicator CHannels (PHICHs) in response to respective receptions of data TBs transmitted from the UEs to RPs.

Typically, the PDCCHs are a major part of the total DL overhead in the communication system. There are various methods for reducing this overhead, and a typical method for reducing this overhead is to scale its size according to the resources required to transmit the PDCCHs and PHICHs. Assuming Orthogonal Frequency Division Multiple Access (OFDMA) schemed used for a DL transmission in the communication system, a Control Channel Format Indicator (CCFI) parameter can be transmitted through the Physical Control Format Indicator CHannel (PCFICH) to indicate the number of Orthogonal Frequency Division Multiplexing (OFDM) symbols allocated to the DL control region during a DL Transmission Time Interval (TTI).

FIG. 1 schematically illustrates a structure of a downlink control region included in a downlink TTI according to a conventional mobile communication system.

Prior to the description of FIG. 1 , a structure a DL control region in FIG. 1 in a DL TTI which for simplicity is assumed to consist of one sub-frame having MOFDM symbols.

Referring to FIG. 1, the DL control region occupies the first N sub-frame symbols among OFDM symbols (110). Here, an OFDM symbol is called as a 'sub-frame symbol'. That is, the DL control region is used for transmitting a PDCCH signal. The remaining M-N OFDM symbols are primarily used for transmitting PDSCH signals (120). That is, a region used for transmitting the PDSCH signal is the DL data region. The PCFICH signal is transmitted through some sub-carriers in the first OFDM symbol among M OFDM symbols, and conveys 2 bits indicating a PDCCH size of M=l, or M=2, or M=3 sub-frame symbols. The PCFICH signal is transmitted through a PCFICH Resource Element (RE).

The PHICH signal is also transmitted in some REs of the first sub-frame symbol among M OFDM symbols, and the REs through which the PHICH signal is transmitted are PHICH REs (140). Moreover, some sub-frame symbols among MOFDM symbols also contain RS REs, 150 and 160, that are common to all UEs for each of the transmitter antennas which in FIG. 1 are assumed to be two. The main purposes of the UE-Common RS (CRS) are to enable a UE to obtain a channel estimate result for its DL channel medium and to perform other measurements and functions as they are known in the art. The remaining REs in the DL control region are used to transmit a PDCCH signal.

Meanwhile, PDCCH signals conveying SAs are not transmitted at predetermined locations in a DL control region and, as a consequence, each UE needs to perform multiple decoding operations to determine whether it has a SA in a DL sub-frame. To assist a UE which should perform the multiple decoding operations, the REs carrying each PDCCH signal are grouped into Control Channel Elements (CCEs) in the logical domain. For a given number of DCI format bits, the number of CCEs used for a DCI format transmission depends on the channel coding rate (here, a Quadrature Phase Shift Keying (QPSK) scheme is assumed as a modulation scheme).

For UEs experiencing low or high Signal-to-Interference and Noise Ratio (SINR) in a DL, serving TPs may respectively use a relatively low or relatively high channel coding rate for the PDCCH signal transmission in order to achieve a desired BLock Error Rate (BLER). Therefore, a PDCCH signal transmission to a UE experiencing relatively low DL SINR may typically require more CCEs that a PDCCH signal transmission to a UE experiencing relatively high DL SINR (here, different power boosting schemes may also be applied to REs used for a CCE transmission). Here, typical CCE aggregation levels used for the PDCCH signal transmission are, for example, of 1, 2, 4, and 8 CCEs.

For a PDCCH decoding process, a UE may determine a search space for PDCCH candidates, after it restores the CCEs in the logical domain, according to a common set of CCEs for all UEs (UE Common Search Space or UE-CSS) and according to a UE-dedicated set of CCEs (UE-Dedicated Search Space or UE- DSS). The UE-CSS may consist of the first N_C ^U _C ^E _E ^CSS CCEs in the logical domain. The UE-DSS may be determined according to a pseudo-random function having as inputs UE-common parameters, such as the sub-frame number or the total number of CCEs included in the sub-frame, and UE-specific parameters such as the UE identity (UE ID). For example, for CCE aggregation levels ι e {1,2,4,8} , the CCEs for PDCCH candidate m are determined by Math Figure 1.

[Math Fi ure 1 ]

where N_CCEJl is the total number of CCEs included in sub-frame k , i = o,—, L - \ , m = o,- - - , M ⁾ - \ , M^(l) is the number of PDCCH candidates to monitor in a search space, and [_ J is the "floor" function rounding a number to its immediately smaller integer. Exemplary values of M^(L) for L <≡ {1,2,4,8} are, respectively, {0, 0, 4, 2} in the UE-CSS, and {6, 6, 2, 2} in the UE-DSS. For the UE-CSS, Y_K = 0 . For the UE-DSS, Y_K = A - Y_K__X ) mod D where Y__] = UE_ID≠O ,

A = 39827 and£> = 65537 .

PDCCHs conveying information to multiple UEs, such as for example a PDCCH conveying Transmission Power Control (TPC) commands for UEs to adjust their PUSCH or PUCCH transmission powers, are transmitted in the UE- CSS. Additionally, if enough CCEs remain in the UE-CSS after the transmission of PDCCHs conveying DCI to multiple UEs in a sub-frame, the UE-CSS may also be used to transmit PDCCH conveying SAs with some specific DCI formats. The UE-DSS is exclusively used to transmit PDCCHs providing SAs. For example, the UE-CSS may consist of 16 CCEs and support 2 PDCCHs with 1 = 8 CCEs, or 4 PDCCHs with L = 4 CCEs, or 1 PDCCH with i = 8 CCEs and 2 PDCCHs with 1 = 4 CCEs. The CCEs for the UE-CSS are placed first in the logical domain prior to interleaving operation.

FIG. 2 schematically illustrates a PDCCH transmission process in a conventional mobile communication system.

Referring to FIG 2, after performing a channel coding and a rate matching, a Node B the encoded bits of DCI formats maps to CCEs in a logical domain. The first 4 CCEs ( L = 4), CCE1 201, CCE2 202, CCE3 203, and CCE4 204 are used for transmitting a PDCCH signal to UE 1. The next 2 CCEs ( L = 2 ), CCE5 211 and CCE6 212, are used for transmitting a PDCCH signal to UE2. The next 2 CCEs (z = 2 ), CCE7 221 and CCE8 222, are used for transmitting a PDCCH signal to UE3. Finally, the last CCE (l = l ), CCE9 231, is used for transmitting a PDCCH signal to UE4.

DCI format bits applied to a PDCCH may be scrambled 240 with a binary scrambling code (cell-specific bit scrambling)(240). The cell-specific bit scrambled DCI format is modulated using a modulation scheme, e.g., a QPSK scheme (QPSK modulation)(250). Each CCE is further divided into Resource Element Groups (REGs), and CCEs included in a REG is called as mini-CCEs. For example, a CCE consisting of 36 REs can be divided into 9 REGs, each consisting of 4 REs.

The QPSK modulated DCI format is interleaved using a preset interleaving scheme (260). The interleaving is applied among REGs (blocks of 4 QPSK symbols). For example, a block interleaver may be used where the interleaving is performed on symbol-quadruplets (4 QPSK symbols corresponding to the 4 REs included in a REG) instead of on individual bits. After interleaving the REGs, the resulting series of QPSK symbols are shifted by J symbols (270), and finally each QPSK symbol is mapped to an RE in the DL control region included in a sub-frame (280). The number of shifted symbols may be different for each cell.

Therefore, in addition to the RS from the TP antenna port REs 291 and 292, and other control channels such as a PCFICH or a PHICH 293, the REs in the DL control contain QPSK symbols corresponding to DCI format for UEl 294, UE2 295, UE3 296, and UE4 297.

FIG. 3 schematically illustrates a PUSCH transmission process in a conventional mobile communication system. For simplicity, it is assumed that a Transmission Time Interval (TTI) is consists of one sub-frame 310 which includes two slots. Each slot, e.g., a slot 320 includes N^^u _mb OFDM symbols used for the transmission of data signals, UCI signals, or RSs. Each OFDM symbol included in each slot, e.g. , an OFDM symbol 330 includes a Cyclic Prefix (CP) to mitigate interference due to channel propagation effects.

The PUSCH transmission in one slot may be either at the same BW or at a different BW than the PUSCH transmission in the other slot. Some OFDM symbols in each slot are used to transmit RS 340 which enables channel estimation and coherent demodulation of the received data and/or UCI signals. The transmission B W consists of frequency resource units which may be referred to as Physical Resource Blocks (PRBs).

Each PRB consists of N s^mc sub-carriers, ³ or REs, ⁷ and a UE is allocated P_USCH PRBs 350 for a total of M™^scu = M_PUSCH · REs for the PUSCH transmission BW. The last sub-frame symbol may be used for the transmission of Sounding Reference Signal (SRS) 360 from one or more UEs. The main purpose of the SRS is to provide the Node B a CQI estimate for a UL channel medium for the respective UE. The SRS transmission parameters for each UE are semi-statically configured by the Node B through higher layer signaling.

The number of sub-frame symbols available for data transmission is ^Nsy^Um ^H = ² - {^Nymb - ^])- ^Nsits > where Nm = ¹ ^ ^me last sub-frame symbol is used for SRS transmission and N„„„ = o otherwise. FIG. 4 schematically illustrates a structure of a signal transmission apparatus in a conventional mobile communication system.

A signal transmission apparatus in FIG. 4 schematically illustrates an exemplary structure of a signal transmission apparatus for transmitting data, CSI, and HARQ-ACK signals through a PUSCH.

Referring to FIG. 4, the signal transmission apparatus includes a multiplexer 420, a puncturer/inserter 430, a Discrete Fourier Transform (DFT) unit 440, a sub-carrier mapper 450, a transmission BW controller 455, an Inverse Fast Fourier Transform (IFFT) unit 460, a CP inserter 470, and a filter 480.

Coded bits 405 and coded data bits 410 are input to the multiplexer 420, the multiplexer 420 multiplexes the coded bits 405 and the coded data bits 410 based on a preset multiplexing scheme and outputs the multiplexed signal to the puncturer/inserter 430. The puncturer/inserter 430 punctures the multiplexed signal based on a preset puncturing scheme, inserts HARQ-ACK bits into the punctured signal, and outputs the HARQ-ACK bit inserted signal to the DFT unit 440. The DFT unit 440 performs a DFT operation on the HARQ-ACK bit inserted signal and the DFT processed signal to the sub-carrier mapper 450.

The sub-carrier mapper 450 performs a sub-carrier mapping operation on the DFT processed signal based on a preset sub-carrier mapping scheme and outputs the sub-carrier mapped signal to the IFFT unit 460. The sub-carrier mapping scheme is determined by the transmission BW controller 455, and the sub-carrier mapper 450 performs the sub-carrier mapping operation on selected REs corresponding to a PUSCH transmission BW among REs.

The IFFT unit 460 performs an IFFT operation on the signal output from the sub-carrier mapper 450 and outputs the IFFT processed signal to the CP inserter 470. The CP inserter 470 inserts a CP into the signal output from the IFFT unit 460 and outputs the CP inserted signal to the filter 480. The filter 480 filters the signal output from the CP inserter 470 based on a preset filtering scheme and outputs a transmission signal 490. In the signal transmission apparatus in FIG. 4, for brevity, an additional transmitter circuitry such as a digital-to-analog converter, analog filters, amplifiers, and transmitter antennas is not illustrated.

Also, in the signal transmission apparatus in FIG. 4, an encoding process for the data bits and the CSI bits, as well as a modulation process for all transmitted bits, are omitted for brevity. The PUSCH transmission is assumed to be over clusters of contiguous REs in accordance to the DFT Spread Orthogonal Frequency Multiple Access (DFT-S-OFDM) scheme allowing signal transmission over one cluster 495A (also known as Single-Carrier Frequency Division Multiple Access (SC-FDMA) scheme), or over multiple non-contiguous clusters 495B.

FIG. 5 schematically illustrates a structure of a signal reception apparatus in a conventional mobile communication system.

Referring to FIG. 5, the signal reception apparatus includes a filter 520, a CP remover 530, a Fast Fourier Transform (FFT) unit 540, a sub-carrier de- mapper 550, a reception BW controller 555, an Inverse Discrete Fourier Transform (IDFT) unit 560, an ACK/NACK extractor 570, and a de-multiplexer 580.

A Radio-Frequency (RF) analog signal received through an antenna is generated as a digital signal 510 by processing through further processing units (such as filters, amplifiers, frequency down-converters, and analog-to-digital converters) which are not shown for brevity, and the digital signal 510 is input to the filter 520. The filter 520 filters the digital signal 510 based on a preset filtering scheme and outputs the filtered signal to the CP remover 530. The CP remover 530 removes a CP from the signal output from the filter 520, and outputs the CP removed signal to the FFT unit 540.

The FFT unit 540 performs an FFT operation on the signal output from the CP remover 530 and outputs the FFT processed signal to the sub-carrier de- mapper 550. The sub-carrier de-mapper 550 performs an sub-carrier de- mapping operation on the signal output from the FFT unit 540 and outputs the sub-carrier de-mapped signal to the IDFT unit 560. Here, a sub-carrier de- mapping scheme is determined by the reception BW controller 555, and the sub- carrier de-mapper 550 performs the sub-carrier de-mapping operation on selected REs corresponding to a PUSCH transmission BW used in the signal transmission apparatus among REs.

The IDFT unit 560 performs an IDFT operation on the signal output from the sub-carrier de-mapper 550 and ouputs the IDFT processed signal to the ACK/NACK extractor 570. The ACK/NACK extractor 570 extracts ACK/NACK information from the signal output from the IDFT unit 560 and outputs the ACK/NACK information to the de-multiplexer 580. The demultiplexer 580 de-multiplexes the ACK/NACK information using a preset de- multiplexing scheme and outputs data bits 590 and CSI bits 595. In the signal reception apparatus, well known receiver functionalities such as channel estimation, demodulation, and decoding are not shown for brevity.

In order to support higher data rates than possible in legacy communication systems, aggregation of multiple Component Carriers (CCs) (which is called as carrier aggregation (CA)) is considered in both the DL and the UL to provide higher operating BWs. For example, to support communication over 60 MHz, aggregation of three 20 MHz CCs can be used.

FIG. 6 schematically illustrates a principle of CC aggregation in a conventional mobile communication system.

Referring to FIG. 6, an operating DL BW of 60 MHz 610 is constructed by the aggregation of 3 (contiguous, for simplicity) DL CCs, 621, 622, 623, each having a BW of 20 MHz. Similarly, an operating UL BW of 60 MHz 630 is constructed by the aggregation of 3 UL CCs, 641, 642, 643, each having a BW of 20 MHz. For simplicity, in FIG. 6, each DL CC is assumed to be uniquely mapped to an UL CC (symmetric CC aggregation) but it is also possible for more than 1 DL CC to be mapped to a single UL CC or for more than 1 UL CC to be mapped to a single DL CC (asymmetric CC aggregation, not shown for brevity). The link between DL CCs and UL CCs is typically UE-specific.

The Node B configures CCs to a UE using higher layer signaling, such as for example Radio Resource Control (RRC) signaling. The RRC-configured DL CCs can be activated or deactivated by Medium Access Control (MAC) signaling or PHYsical (PHY) layer signaling (activation/deactivation for each RRC- configured UL CC is determined by the activation/deactivation of its linked DL CC). Activation of a DL (UL) CC for a UE means that the UE can receive a PDSCH signal (transmit a PUSCH signal) in that CC; the reverse applies for deactivation of a DL (UL) CC.

In order to maintain communication, one DL CC, and one UL CC linked to that the DL CC, need to remain activated and they may be respectively referred to as a DL Primary CC (DL PCC) and a UL Primary CC (UL PCC).

Aperiodic CSI report via a PUSCH is triggered by a CSI Request field in a PDCCH. In following description, the serving cell is corresponding to each CC. If an indication sent in the scheduling grant for a serving cell c is decoded, aperiodic CSI reporting is performed using the PUSCH on the serving cell c. If the CQI request field is implemented with 1 bit, a report is triggered if a field value of the CQI request field is set to T. If the CQI request field is implemented with 2 bits, a report through the PUSCH is triggered as Table 1.

Meanwhile, if a field value of a Carrier Indicator Field (CIF) is ' 1 ' (bits '001'), and a field value of a CSI Request field is ' 1 ' (bits '01'), then a CSI of a DL CC 1 which is linked to a UL CCl due to the CIF is feedback to a Node B. If a field value of the CSI Request field is '2' (bits ΊΟ'), then depending on the higher layer configuration, the CSI(s) of DL CC(s) is/are feedback to the Node B.

Downlink transmissions of a Long Term Evolution (LTE) mobile communication system and a Long Term Evolution Advanced (LTE-A) mobile communication system are made in units of sub-frames in a time domain and Resource Blocks (RBs) in a frequency domain. A sub-frame equals to 1 msec of transmission time while an RB equals to 180kHz of transmission bandwidth consisting of 12 subcarriers.

FIG. 7 schematically illustrates a structure of a time domain and a frequency domain in a conventional LTE-A mobile communication system.

A system bandwidth of the LTE-A mobile communication system consists of multiple RBs in the frequency domain and multiple sub-frames in the time domain as depicted in FIG. 7.

In a mobile communication system using an LTE-A Release 10 and releases following the LTE-A Release 10, in a downlink, the following RSs are transmitted: . Cell Specific Reference Signal (CRS): Used for initial system access, paging, PDSCH demodulation, channel measurement, handover, etc

. Demodulation Reference Signal (DMRS): Used for demodulation of a PDSCH signal

. Channel Status Information Reference Signal (CSI-RS): Used for channel measurement

In addition to the RSs, a zero-power CSI-RS can be applied in an LTE-A Release 10. The zero-power CSI-RS can occur in the same time and frequency resources as a CSI-RS but differ from a CSI-RS in that there is no signal transmitted on REs which are subject to the zero-power CSI-RS. The purpose of the zero-power CSI-RS is to not transmit on resources which are used by neighboring TPs for a CSI-RS transmission so as not to generate interference on these CSI-RSs transmitted by neighboring TPs. The resources which are used for a transmission of the RSs, the zero power CSI-RS, the PDSCH signal, and the control channels are depicted in FIG. 8.

FIG. 8 schematically illustrates locations of resources used for RSs, a PDSCH signal, zero power CSI-RS, and control channel signals in a conventional LTE-A mobile communication system.

Note a diagram in FIG. 8 is for a single RB in a frequency domain for a single sub-frame in a time domain. For each sub-frame, multiple RBs may exist and the signals can be transmitted through multiple RBs in a similar manner as shown in FIG. 8.

The resources marked by alphabets A, B, C, D, E, F, G, H, I, J in FIG. 8 corresponds to locations where transmission for a CSI-RS using 4 antenna ports. For example, in 4 REs marked by Ά', A CSI-RS using 4 antenna ports can be transmitted. A CSI-RS using 2 antenna ports can be transmitted on resources which are obtained by dividing the resources for a CSI-RS using 4 antenna ports into 2. Additionally, a CSI-RS using 8 antenna ports can be transmitted on resources which are obtained by combining the 2 resources for a CSI-RS using 4 antenna ports. A zero-power CSI-RS can be applied on the resources for a CSI- RS using 4 antenna ports.

In the LTE-A mobile communication system, there is a need for a method of receiving a downlink data channel signal, e.g., a PDSCH signal by considering a RS resource, a SYNC signal resource, and a PBCH resource allocated in each of a plurality of cells in order to effectively use a CoMP scheme. The RS resource denotes a resource through which a RS is transmitted, the SYNC signal resource denotes a resource through which the SYNC signal is transmitted, and the PBCH resource denotes a resource through which the PBCH signal is transmitted.

In the LTE-A mobile communication system using the CoMP scheme, there is a need for distinguishing a sub-frame through which a PDSCH signal is transmitted among sub-frames transmitted from a plurality of cells and a sub- frame through which a PDSCH signal is not transmitted among the sub-frames in order that the UE effectively receives the PDSCH signal.

Further, in the LTE-A mobile communication system using the CoMP scheme, if a Multi-User Multiple Input Multiple Output (MU-MIMO) scheme is used, different scrambling sequences may be used for different TPs in order to enhance a DMRS capacility.

Therefore, there is a need for identifying DMRS scrambling schemes used for each TP in the LTE-A mobile communication system using the CoMP scheme.

SUMMARY OF THE INVENTION

An embodiment of the present invention proposes an apparatus and method for transmitting/receiving a RS in a cellular radio communication system using a CoMP scheme.

Another embodiment of the present invention proposes an apparatus and method for transmitting/receiving a DMRS in a cellular radio communication system using a CoMP scheme.

Further another embodiment of the present invention proposes an apparatus and method for transmitting/receiving a DMRS by considering an antenna port in a cellular radio communication system using a CoMP scheme.

Still another embodiment of the present invention proposes an apparatus and method for transmitting/receiving a DMRS based on a DMRS scrambling sequence in a cellular radio communication system using a CoMP scheme.

In accordance with one aspect of the present invention, there is provided a method for transmitting a DeModulation Reference Signal (DMRS) by a Node B in a cellular radio communication system using a Cooperative Multi-Point (CoMP) scheme. The method includes for at least one antenna port, transmitting a DMRS based on a preset DMRS scrambling sequence, wherein the DMRS scrambling sequence is initialized with an initial value at a start of each sub-frame, and wherein the initial value is determined using an identifier of the DMRS scrambling sequence, a slot number of a serving (or primary) cell of a related User Equipment (UE), a sub-frame offset value based on the DMRS scrambling sequence, and a parameter related to a cell identifier of a cell for which the related UE has reported a Reference Signal Received Power (RSRP) at least once

In accordance with another aspect of the present invention, there is provided a method for receiving a DeModulation Reference Signal (DMRS) by a User Equipment (UE) in a cellular radio communication system using a Cooperative Multi-Point (CoMP) scheme. The method includes receiving a DMRS from a Node B, wherein, for at least one antenna port, the DMRS is transmitted based on a preset DMRS scrambling sequence, wherein the DMRS scrambling sequence is initialized with an initial value at a start of each sub- frame, and wherein the initial value is determined using an identifier of the DMRS scrambling sequence, a slot number of a serving (or primary) cell of a related UE, a sub-frame offset value based on the DMRS scrambling sequence, and a parameter related to a cell identifier of a cell for which the related UE has reported a Reference Signal Received Power (RSRP) at least once.

In accordance with further another aspect of the present invention, there is provided a Node B in a cellular radio communication system using a Cooperative Multi-Point (CoMP) scheme. The Node B includes a transmitter for transmitting a DeModulation Reference Signal (DMRS) based on a preset DMRS scrambling sequence, for at least one antenna port, wherein the DMRS scrambling sequence is initialized with an initial value at a start of each sub- frame, and wherein the initial value is determined using an identifier of the DMRS scrambling sequence, a slot number of a serving (or primary) cell of a related User Equipment (UE), a sub-frame offset value based on the DMRS scrambling sequence, and a parameter related to a cell identifier of a cell for which the related UE has reported a Reference Signal Received Power (RSRP) at least once.

In accordance with still another aspect of the present invention, there is provided a User Equipment (UE) in a cellular radio communication system using a Cooperative Multi-Point (CoMP) scheme. The UE includes a receiver for receiving a DeModulation Reference Signal (DMRS) from a Node B, wherein, for at least one antenna port, the DMRS is transmitted based on a preset DMRS scrambling sequence, wherein the DMRS scrambling sequence is initialized with an initial value at a start of each sub- frame, and wherein the initial value is determined using an identifier of the DMRS scrambling sequence, a slot number of a serving (or primary) cell of a related UE, a sub-frame offset value based on the DMRS scrambling sequence, and a parameter related to a cell identifier of a cell for which the related UE has reported a Reference Signal Received Power (RSRP) at least once.

As is apparent from the foregoing description, an embodiment of the present invention enables a DMRS transmission/reception in a cellular radio communication system using a CoMP scheme.

An embodiment of the present invention enables a DMRS transmission/reception with consideration for an antenna port in a cellular radio communication system using a CoMP scheme.

An embodiment of the present invention enables a DMRS transmission/reception based on a DMRS scrambling sequence in a cellular radio communication system using a CoMP scheme.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a structure of a downlink control region included in a downlink TTI according to a conventional mobile communication system;

FIG. 2 schematically illustrates a PDCCH transmission process in a conventional mobile communication system;

FIG. 3 schematically illustrates a PUSCH transmission process in a conventional mobile communication system;

FIG. 4 schematically illustrates a structure of a signal transmission apparatus in a conventional mobile communication system;

FIG. 5 schematically illustrates a structure of a signal reception apparatus in a conventional mobile communication system;

FIG. 6 schematically illustrates a principle of CC aggregation in a conventional mobile communication system;

FIG. 7 schematically illustrates a structure of a time domain and a frequency domain in a conventional LTE-A mobile communication system;

FIG. 8 schematically illustrates locations of resources used for RSs, a PDSCH signal, zero power CSI-RS, and control channel signals in a conventional LTE-A mobile communication system;

FIG. 9 schematically illustrates a cell structure in which each cell has a unique Cell-ID and slot number in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention;

FIGs. lOA to 10B schematically illustrate a MU-MIMO transmission in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention;

FIG. 11 schematically illustrates RB structures for Cell-1 and Cell-2 which have different CRS starting positions in an LTE-A mobile communication system;

FIG. 12 schematically illustrates a RB structure if a JT scheme is used between a Cell-1 and a Cell-2 in an LTE-A mobile communication system;

FIG. 13 schematically illustrates a sub-frame structure in a case where 2 cells use different MBSFN sub-frame configurations in an LTE-A mobile communication system;

FIG. 14 schematically illustrates a rate-matching scheme for a JT scheme in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention;

FIG. 15 schematically illustrates a puncturing scheme for a JT scheme in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention;

FIG. 16 is a flowchart illustrating an example of a method for receiving a PDSCH signal in a UE in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention;

FIG. 17 is a flowchart illustrating another example of a method for receiving a PDSCH signal in a UE in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention;

FIG. 18 is a flowchart illustrating still another method for receiving a PDSCH signal in a UE in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention; FIG. 19 schematically illustrates an internal structure of a UE in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention;

FIG. 20 schematically illustrates an internal structure of a Node B in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the following description, specific details such as detailed configuration and components are merely provided to assist the overall understanding of exemplary embodiments of the present invention. Therefore, it should be apparent to those skilled in the art that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

An embodiment of the present invention proposes an apparatus and method for transmitting/receiving a Reference Signal (RS) in a cellular radio communication system using a Cooperative Multi-Point (CoMP) scheme.

Another embodiment of the present invention proposes an apparatus and method for transmitting/receiving a DeModulation Reference Signal (DMRS) in a cellular radio communication system using a CoMP scheme.

Still another embodiment of the present invention proposes an apparatus and method for transmitting/receiving a DMRS by considering a DMRS scrambling sequence in a cellular radio communication system using a CoMP scheme.

Embodiments of the present invention will be described below with reference to a Long Term Evolution Advanced (LTE-A) mobile communication system based on an Orthogonal Frequency Division Multiplexing (OFDM) scheme. However, it will be understood by those of ordinary skill in the art that embodiments of the present invention may be applied to any one of a High Speed Downlink Packet Access (HSDPA) mobile communication system, a High Speed Uplink Packet Access (HSUPA) mobile communication system, a Long-Term Evolution (LTE) mobile communication system, a High Rate Packet Data (HRPD) mobile communication system proposed in a 3^rd Generation Project Partnership 2 (3GPP2), an Institute of Electrical and Electronics Engineers (IEEE) 802.16m mobile communication system, etc.

For convenience, it will be assumed that the LTE-A mobile communication system provides a service to a User Equipment (UE) using a CoMP scheme.

In an LTE Release 9 and an LTE Release 10, a DMRS sequence r{m) of antenna ports p e {7,8,..., + 6} is defined by Math Figure 2.

[Math Figure 2]

1 1 „ .„ -l normal cyclic prefix

J2 V2

- l extended cyclic prefix

Where, a pseudo-random sequence c(0 is defined in Section 7.2 of 3 GPP TS 36.211 vlO.1.0, "E-UTRA, Physical channels and modulation." A pseudo-random sequence generator may be initialised with Math Figure 3 at the start of each sub- frame.

[Math Figure 3]

Cfadt = i«s /2j+l)- (2 ' +l)- 2¹⁶ + «_SCID

Where, a value of «_SCID is zero unless specified otherwise. For a Physical Downlink Shared Channel (PDSCH) signal transmission on a port 7 or a port 8, «_SCID is determined by a DL Control Information (DCI) format 2B or a DCI format 2C associated with the PDSCH signal transmission. The DCI format 2B or a DCI format 2C is defined by 3 GPP TS 36.212 vlO.1.0, "E-UTRA, Multiplexing and Channel coding." In the case of DCI format 2B, «_SCID is indicated by a scrambling identity field according to Table 6.10.3.1-1 in 3GPP TS 36.211 vl 0.1.0, "E-UTRA, Physical channels and modulation." In the case of DCI format 2C, n_scm is given by Table 5.3.3.1.5C-1 in 3 GPP TS 36.212 vlO.1.0, "E-UTRA, Multiplexing and Channel coding." Also, «_SCID is a scrambling identifier and N is a Cell Identifier (Cell-ID) of the cell which is serving the UE. That is, LTE Release 9 and 10 DMRS scrambling is based on «_s , N{g" (Cell-ID) , and «_SCID , where «_s is a slot number of a serving cell of the UE and determined by the UE detecting the serving cell's PSS (Primary Synchronization Signal) or/and SSS (Secondary Synchronization Signal).

Note that, in an LTE mobile communication system, each cell in a multi- cell system can have its own Cell-ID and slot number resulting in different DMRS scrambling sequences among those cells.

FIG. 9 schematically illustrates a cell structure in which each cell has a unique Cell-ID and slot number in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention. In the cell structure in FIG. 9, each of 3 cells has its own Cell-ID and slot number.

A description of a DMRS scrambling for a DL CoMP scheme will be followed.

Improving coverage and cell-edge throughput are key objectives in communication systems. A CoMP transmission/reception scheme, i.e., a signal transmission/reception scheme using a CoMP scheme is an important scheme to achieve these objectives. The CoMP scheme relies on the fact that when a UE is in a cell-edge region, it may be able to reliably receive signals from a set of Transmission Points (TPs) (DL CoMP) and reliably transmit signals to a set of Reception Points (RPs) (UL CoMP).

DL CoMP schemes can range from simple ones of interference avoidance, such as a coordinated scheduling, to more complex ones requiring accurate and detailed channel information such as joint transmission from multiple TPs. UL CoMP schemes can also range from simple ones where a PUSCH scheduling is performed considering a single RP to more complex ones where the received signal characteristics and the generated interference at multiple RPs are considered.

Support of a DL CoMP scheme introduces a new Channel State Information (CSI) feedback scheme for various CoMP schemes. As a legacy CSI feedback scheme considers only one TP and one Channel State Information Reference Signal (CSI-RS) for a channel measurement and a CSI feedback report, it is not possible to support the CoMP schemes from multiple transmission points which utilize multiple CSI-RSs. For this reason, an additional CSI feedback scheme for multiple TPs (or a CSI feedback scheme for corresponding CSI-RS configurations) is required to support DL CoMP schemes. Further, feedback for CoMP schemes can be categorized as follows.

. Multiple CSI reports for multiple TPs (transmission point)

- Node B configures multiple CSI-RS configurations to a UE for CSI reports.

- Each CSI-RS configuration corresponds to a specific TP.

. The case where one CSI-RS configuration corresponds to multiple TPs is also included.

- The set of multiple CSI-RS configurations (or the corresponding TPs) for CSI reports is defined as "CoMP measurement set)"

- Each CSI report corresponds to a CSI-RS configuration for a TP

. Additional feedback for dynamic point selection with a dynamic blanking (DS/DB) scheme

- Some TPs (e.g. macro Node B) can be turned off (blanking) in order to help downlink data reception of UEs attached to other TPs

- One UE needs to feedback additional CSI for blanking

. Additional feedback for a joint transmission (JT) scheme

- Multiple TPs can simultaneously transmit data for one UE.

- JT may require additional CSI for a co-transmission scheme from multiple TPs

In order to support a Multi-User Multiple Input Multiple Output (MU- MIMO) scheme with in a TP, the same scrambling sequence can be used for DMRS. For example, a TP can support a MU-MIMO scheme with orthogonal DMRS ports by using the same scrambling scheme for DMRS and allocating port 7 and port 8 to two UEs. On the other hand, in order to enhance DMRS capacity, for different TPs, different scrambling sequences can be used for DMRS. For example, a scrambling sequence used in a TP 1 may be different from a scrambling sequence used in a TP2.

In a CoMP scheme, network can decide to transmit a PDSCH signal to a UE using different TPs which could belong to different cells having different Cell-IDs and slot numbers. Additionally, a MU-MIMO scheme including the UE could occur over the different TPs.

FIGs. 10A to 10B schematically illustrate a MU-MIMO transmission in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention. For example, FIGs. 10A to 10B show two different MU-MIMO transmissions for UE-2 configured as a CoMP UE who can be served by Cell-0 and/or Cell-1

Referring to FIGs. 10A to 10B, In FIG. 10A, enhanced Node B (eNB) decides to schedule MU-MIMO transmission from Cell-0 where UE2 is paired with UEl in Cell-0 while it decides to schedule a MU-MIMO transmission from Cell-1 where UE2 is paired with UE3 served by Cell-1 in FIG. 10B. In the case of FIG. 10A, UE2 would be better to use a DMRS scrambling scheme for Cell-0 in order to use an orthogonal DMRS port with the same DMRS scrambling scheme as UEl.

On the other hand, in the case of FIG. 10B, UE2 would be better to use a DMRS scrambling scheme for Cell-1 in order to use an orthogonal DMRS port with the same DMRS scrambling scheme as UE3. That is, the scrambling sequence applied to the DMRS has to be dynamically adapted to provide an orthogonality depending on which MU-MIMO is made. Therefore, UE has to determine the following information in a dynamic manner.

. Cell-ID: an integer value in the range of [0, 503]

. Slot number: an integer value in the range of [0, 20]

. «_SCID : an integer value in the range of [0, 1]

In a scheme to realize a dynamic adaptation of a DeModulation Reference Signal (DMRS) scrambling sequence, an initialization value of the DMRS scrambling sequence as expressed in Math Figure lis used for a UE:

[Math Figure 4]

¾* = /2J+ 1)· (2^ + 1)· 2¹⁶ + ¾„₀ where «_SC/D is a scrambling identifier and is dynamically determined by DCI between 0 and 1 such as an LTE Release 10. Another parameter «_s,nsao in Math Figure 4 is given by Math Figure 4. [Math Figure 5] η r,

s>ⁿSCID = n ^s„ + 2A ⁿ„SCID mod20 where n_s is a slot number of a serving (or primary) cell of the UE, and A„_saD is a sub-frame offset value depending on n_SCID in a range of size 10 such as [0, 9] or [-4, 5].

One way to determine the parameters n,„ and x„ is to use Table 2 where Dl, XI, D2, and X2 are signaled by higher layer. That is, after two pairs of (Dl, XI) and (D2, X2) are configured to a UE by higher layer signaling, the UE may use n_SCID derived in DCI to determine one of the two pairs in one sub- frame scheduled for a PDSCH signal transmission.

[Table 2]

In Table 2, x„_sao and Δ_¾αο for n_SCID are expressed.

In another way to determine parameters n_{s nscm} and x„ X„ is determined by Table 3 where XI and X2 are signaled by higher layer and n_s„_scm is determined as follows:

. If x„_saD = Nf -' , the UE uses the slot number of Cell-/.

. If x_nscm≠ N%"^~' for all , the slot number is set to a default value (e.g., ⁿ _{* n} =o)- where

are the Cell-IDs of the cells Cell-1, Cell-2 Cell-M for which the UE reported Reference Signal Received Power (RSRP) at least once, or the Cell-IDs in the list of physical Cell-IDs which is signaled by an eNB.

[Table 3] ⁿSClD

0 XI

1 X2

In Table 3, x„_sao for n_SCID is expressed.

In other alternative to realize a dynamic adaptation of the DMRS scrambling sequence, the following initialization value of the DMRS random sequence as expresses in Math Figure 6 is used for a UE:

[Math Figure 6]

¾ ini_tt X n_nSCID2 + l ))- 2 16 + n SCID where n_sclD is dynamically determined by DCI for a PDSCH scheduling between 0 and 1 like as an Release 10 and n_SCID2 s an additional dynamic parameter determined by DCI for PDSCH scheduling among the integers in the range of [0, N-l]. _¾ao and n_SC!D2 can be derived in different two DCI fields or one DCI field jointly coded in DCI format for PDSCH scheduling. If n_SCID and n_SCID2 have different fields, n_SCID would derived from legacy 3 -bit field indicating antenna port(s), scrambling identity, and number of layers and ⁿsciD2 would be derived from one bit field or two bits field with N=2 or N=4, respectively.

On the other hand, if n_SCID and «_sao2 are jointly coded in one DCI field, n_sclD and «_sc/£)2 would be derived from 3, 4 or 5 -bit field indicating antenna port(s), scrambling identity ( n_SCID ), n_SCID2 , and number of layers. Another parameter n _n in Math Figure 6 is given by «_?„ = n, + 2A„ mod 20 where n_s is the slot number of the serving (or primary) cell of the UE and Δ_¾α∞ is the sub-frame offset value depending on n_sclD2 in a range of size 10 such as [0, 9] or H, 5].

One way to determine the parameters «_{J ¾ 7D2} and x_nscmi is to use Table 3 where Dl, XI, D2, and X2 are signaled by higher layer. The assumption in Table 4 is that «_SC/D2 is determined between 0 and 1. That is, after two pairs of (Dl, XI) and (D2, X2) are configured to the UE by higher layer signaling, the UE may use n_SCID2 derived in DCI to determine one of the two pairs in one sub- frame scheduled for PDSCH transmission.

[Table 4]

In Table 4, x„_SCID2 and Δ_¾αο2 for n_SCID2 are expressed.

In another way to determine parameters n,„ and x„ , x„ is determined by Table 5 where XI and X2 are signaled by higher layer and «_s„_SO02 is determined as follows:

. If x„ = Ν%"-' , the UE uses the slot number of Cell-/.

. If x„ ≠ Nfn"^'' for all /^' the slot number is set to a default value (e.g. η, . = 0 ).

where Ν%"- Ν%"-²,...,Ν%"-^Μ are the Cell-IDs of the cells Cell-1, Cell-2, ..., Cell-M for which the UE reported RSRP at least once, or the Cell-IDs in the list of physical Cell-IDs which is signaled by an eNB.

[Table 5]

In Table 5, x_nscim for n_SCID2 is expressed.

In other alternative to realize a dynamic adaptation of the DMRS scrambling sequence, the following initialization value of the DMRS scrambling sequence expressed in Math Figure 7 is used for a UE:

[Math Figure 7] ^Cinit -

+ ⁿSCID > where n_SCID is dynamically determined by DCI for a PDSCH scheduling between 0 and 1 like as an LTE Release 10 and «_sao2 is an additional dynamic parameter determined by DCI for PDSCH scheduling among the integers in the range of [0, N-l]. n_scm and n_SCID2 can be derived in different two DCI fields or one DCI field jointly coded in a DCI format for a PDSCH scheduling. If n_SCID and n_SCID2 have different fields, n_SCID would derived from legacy 3-bit field indicating antenna port(s), scrambling identity, and number of layers and n_SCID2 would be derived from one bit field or two bits field with N=2 or N=4, respectively.

On the other hand, if n_sclD and n_sclD2 are jointly coded in one DCI field, n_saD and n_SC!D2 would be derived from 3, 4 or 5 -bit field indicating antenna port(s), scrambling identity ( n_SCID ), n_SCID2 , and number of layers. Another parameter «_{s,(%CTD,¾aD2}) in Math Figure 7 is given by ⁿsXnsao,"saD2) ^{= n}s ⁺

^where. "s is a slot number of a serving (or primary) cell of the UE and Δ_{(¾αο t}„_sam) is the sub-frame offset value depending on the pair of {n_sclD,n_SCID2) in the range of size 10 such as [0, 9] or [-4, 5].

One way to determine the parameters n_s ,„ „ . and x,„ „ , is to use Table 6 where Dl,- D2, D3, D4, XI, X2, X3, and X4 are signaled by higher layer. The assumption in Table 6 is that n_SCID2 is determined between 0 and 1. That is, after four pairs of (Dl, XI), (D2, X2), (D3, X3) and (D4, X4) are configured to the UE by higher layer signaling, the UE may use {n_SCID,n_saD2 ) derived in DCI to determine one of the four pairs in one sub-frame scheduled for a PDSCH transmission.

[Table 6]

(ⁿSClD ' ⁿSClD2 )

(0, 0) Dl XI

(0, 1) D2 X2

(1, 0) D3 X3

(1, 1) D4 X4 In Table 6, x_(¾aDi„_sora)and Δ_{(¾αο>¾σ∞)} for (_%C/D,_%C/D2) are expressed.

In another way to determine parameters «, ₍„ „ ^ and x,„ „ , ^x(»sa_D,»sa_Di) ^ls determined by Table 7 where XI, X2, X3, and X4 are signaled by higher layer and ¾_{¾αο>¾αο2)} is determined as follows:

. If X₍„_saDflscim) = N_/¾"^"'^' , the UE uses the slot number of Cell-/.

. If ^(_¾ao,¾CTD2)≠ Nib⁶"-' f°^{r a}ll the slot number is set to a default value

(^e-g- . ¾,(¾,_oto2) = ⁰ )·

where

are the Cell-IDs of the cells Cell-1, Cell-2, Cell- for which the UE reported RSRP at least once, or the Cell-IDs in the list of physical Cell-IDs which is signaled by an eNB.

[Table 7]

In Table 7, ¾_aD,¾ao2) for (n_SC!D , n_SC!D2 ) is expressed.

In other alternative to realize a dynamic adaptation of the DMRS scrambling sequence, when a UE is scheduled to receive two codewords, the initialization value of the DMRS random sequence is determined between 2 possible values. On the other hand, when the UE is scheduled to receive one codeword, the initialization value of the DMRS random sequence is determined among more than 2 possible values. For the two codewords scheduling, the initialization value is dependent on scrambling identity n_SCID determined by 3- bit field in DCI format for downlink scheduling, while the initialization value is dependent on not only scrambling identity «_SC7D but also additional one bit for the one codeword scheduling.

In an LTE Release 10, a DCI format 2C is used to schedule multiple layer downlink transmissions, where a new data indicator (NDI) field for a disabled Transport Block (TB) is not used as a reserved bit when one codeword scheduling is occurred. Hence NDI field of the disabled transport block in DCI format for downlink scheduling can be reused as the additional one bit for the one codeword scheduling because there is no use of an NDI field for the disabled transport block. For two codeword scheduling, an NDI bit is used for its original purpose of a new data indication. That is, an initialization value of the DMRS random sequence is expressed in Math Figure 8:

[Math Figure 8]

_ ^cinit

^f°^r one codeword scheduling for two codeword scheduling where n_sclD is dynamically determined by DCI between 0 and 1 such as LTE Release 10 and NDI is a new data indicator of a disabled TB determined by DCI between 0 and 1. Additionally, parameters n_{s nscm} and n_{s (¾c;d ND1)} in Math

Figure 8 are given by Math Figure 9 and Math Figure 10, respectively. [Math Figure 9]

n„>ⁿ„SCID = n„+ 2A ⁿ„SCID mod20

[Math Figure 10] nsln_SCID,NDI) = ⁿs + ² (n_saD,NDI) mod20 where n_s is a slot number of a serving (or primary) cell of the UE, and Δ_¾αο and Δ_{(¾αβ Λί£)/)} are a sub-frame offset value depending on n_sclD and (n_SCID,NDJ) , respectively, in a range of size 10 such as [0, 9] or [-4, 5].

One way to determine parameters n_{s lscm} , x„_scm , n_s„_saDrND1) , and ^x(n_saD,N_Dn ^{is t0 use Table 8 where} Dl, XI, D2, X2, D3, X3, D4, X4, D5, X5, D6, and X6 are signaled by higher layer. That is, after six pairs of (Dl, XI), (D2, X2), (D3, X3), (D4, X4), (D5, X5), and (D6, X6) are configured to a UE by higher layer signaling, the UE will use n_SCID or (n_SCID ,NDi) derived in DCI to determine one of the six pairs in one sub-frame scheduled for a PDSCH signal transmission. Note that there can be a dependency among the above six pairs such that ¾_¾αο,ο) = «_¾ ^{and x} _M) =x_nsc!D mandating D1=D5, X1=X5, D3=D6, and X3=X6.

[Table 8]

In another way to determine parameters «_i> x„_sao , «_{s,(¾c;D;WO/)} , and

X(n_SCID,NDi) , x_HsaD and x_(nsciD,_ND1) are determined by Table 9 where XI, X2, X3,

X4, X5 and X6 are signaled by higher layer and »_{i ¾ao} and «₅,₍„_sc;D,wo/) are determined as follows:

. If two codewords are scheduled, n,„ =

. If one codeword is scheduled,

- If x„ = N n"^~l , the UE uses the slot number of Cell-/.

- If x„_scm≠ Nf ^'1 for all /, the slot number is set to a default value (e.g. where

are the Cell-IDs of the cells Cell-1 , Cell-2, Cell-M for which the UE reported RSRP at least once, or the Cell-IDs in the list of physical Cell-IDs which is signaled by an eNB. Note that the parameter of the slot number in the DMRS scrambling for two codewords scheduling is only dependent on that of the serving (or primary) cell of the UE.

Additionally, it is worth to note that there can be a dependency among the six values in Table 9 such that x,_{n 0}, = x„ mandating X1=X5 and X3=X6. [Table 9]

In another way to determine parameters «_{ί ¾αο} , x„_scm , n_sX„_sciD>NDI) , and (_«SC/D>w x_Hscm and X_(nscm,_m!) are determined by Table 9 where XI, X2, X3,

X4, X5 and X6 are signaled by higher layer and «_{s ¾c;d} and n_sirtscm<NDI) are determined as follows:

. If two codewords are scheduled, n_s/lsw = n_s

. If one codeword is scheduled,

- If NDI = 1,

. If x„_saD = N%"-' , the UE uses the slot number of Cell-/.

. If x„_saD≠ N%"^~' for all i, the slot number is set to a default value (e.g. ⁿs,(_nscm,NDI) = ⁰ )·

- IfNDI = 0, n,„ = n_s .

where

are the Cell-IDs of the cells Cell- 1, Cell-2, Cell- for which the UE reported RSRP at least once, or the Cell-IDs in the list of physical Cell-IDs which is signaled by an eNB. Note that the parameter of the slot number in the DMRS scrambling for two codewords scheduling is only dependent on that of a serving (or primary) cell of the UE.

In other alternative to realize a dynamic adaptation of the DMRS scrambling sequence, when a UE is scheduled to receive two codewords, the initialization value of the DMRS random sequence is determined between 2 possible values. On the other hand, when the UE is scheduled to receive one codeword, the initialization value of the DMRS random sequence is determined among more than 2 possible values. For the two codewords scheduling, the initialization value is dependent on scrambling identity n_SCJD determined by 3- bit field in DCI format for downlink scheduling, while the initialization value is dependent on not only scrambling identity n_scm but also additional one bit for the one codeword scheduling.

An NDI field of the disabled TB in a DCI format for a downlink scheduling can be reused as the additional one bit for the one codeword scheduling because there is no use of an NDI field for the disabled TB. For two codeword scheduling, an NDI bit is used for its original purpose of a new data, indication. In this alternative, the initialization value of the DMRS random sequence is expressed as Math Figure 11 :

[Math Figure 11 ]

for one codeword scheduling for two codeword scheduling

where n_sclD is dynamically determined by DCI between 0 and 1 such as an LTE Release 10 and NDI is a new data indicator of the disabled transport block determined by DCI between 0 and 1. The parameter n_{s {nscm ND1)} in Math

Figure 11 is given by ¾_%σο,Μ>/) = n_s +2Δ_{(¾αο>Μ)/)} mod 20 , where n_s is a slot number of a serving (or primary) cell of the UE, and A_(nscwtNDn is a sub-frame offset value depending on (n_SCID,NDi) in a range of size 10 such as [0, 9] or [-4, 5]. Note that the parameter of the slot number in the DMRS scrambling for two codewords scheduling is only dependent on the slot number of the serving (or primary) cell of the UE.

One way to determine parameters x„_saD , n_s„_scm>NDI) , and x₍„_SCID,ND!) is to use Table 10 where Dl, XI, D2, X2, D3, X3, D4, X4, X5, and X6 are signaled by higher layer. That is, for one codeword scheduling, four pairs of (Dl, XI), (D2, X2), (D3, X3), (D4, X4) are configured to a UE by higher layer signaling and then the UE may use (n_SCID , NDi) to determine one of the four pairs in one sub-frame scheduled for PDSCH transmission of one codeword.

On the other hand, for two codewords scheduling, two values of X5 and X6 are configured to the UE by higher layer signaling and then the UE will use n.rm to determine one between X5 and X6 in one sub-frame scheduled for PDSCH transmission of two codeword. Note that there can be a dependency among six values of XI, X2, X6 such that and ^x _(nsciD,o) = ^xn_scm mandating X1=X5 and X3=X6.

[Table 10]

In another way to determine parameters x_nscm , n_s„_scm<mi) , and x_(nsciD>ND1) , x "„sew and X( \ⁿ„saD'^N _N ^L _n"_n) are determined by ^J Table 9 where XI, ' X2, ' X3, ' X4, ' X5 and

X6 are signaled by higher layer and n_{s {nscm DI)} is determined as follows:

. If x„_saD = Nf -' , the UE uses the slot number of Cell-/.

. If x_nscm≠ N%"^~' for all , the slot number is set to a default value (e.g., ⁿs,(»sciD,NDI) = ⁰ )·

where Nf ^~] , Nf ^~2 Nf ^~M are the Cell-IDs of the cells Cell- 1 , Cell-2, Cell-M for which the UE reported RSRP at least once, or the Cell-IDs in the list of physical Cell-IDs which is signaled by an eNB. Note that the parameter of the slot number in the DMRS scrambling for two codewords scheduling is only dependent on that of the serving (or primary) cell of the UE. Additionally, it is worth to note that there can be a dependency among the six values in Table 9 such that x,„ _m =x„ mandating XI =X5 and X3=X6.

In another way to determine parameters x_nscm , n_{s >(¾c;o >M3/)} , and x_{nscw,NDI) , x„ ⁿSClD and \ⁿSClD'ⁿ _m'-"_n I are determined by ·> Table2-2 where XI, X2, X3, X4, X5 and

X6 are signaled by higher layer and n_{slnscm ND1)} are determined as follows:

. IfNDI = 1, - If x_nscm = N%"-' , the UE uses the slot number of Cell-/.

- If x_nsciD≠Ν%"-' for all /, the slot number is set to a default value (e.g.,

. IfNDI = 0, n_{s n} = n_s .

where N%"^~1 , Nf ^~2 N%"^~M are the Cell-IDs of the cells Cell- 1 , Cell-2, Cell- for which the UE reported RSRP at least once, or the Cell-IDs in the list of physical Cell-IDs which is signaled by an eNB. Note that the parameter of the slot number in the DMRS scrambling for two codewords scheduling is only dependent on that of the serving (or primary) cell of the UE.

In other alternative to realize a dynamic adaptation of the DMRS scrambling sequence, when a UE is scheduled to receive two codewords, the initialization value of the DMRS random sequence is determined between 2 possible values. On the other hand, when the UE is scheduled to receive one codeword, the initialization value of the DMRS random sequence is determined among more than 2 possible values. For the two codewords scheduling, the initialization value is dependent on scrambling identity n_sclD determined by 3- bit field in a DCI format for downlink scheduling, while the initialization value is dependent on not only scrambling identity n_SC!D but also additional one bit for the one codeword scheduling.

An NDI field of the disabled TB in a DCI format for downlink scheduling can be reused as the additional one bit for the one codeword scheduling because there is no use of an NDI field for the disabled transport block. For two codeword scheduling, an NDI bit is used for its original purpose of a new data indication. In this alternative, the initialization value of the DMRS random sequence is expressed as Math Figure 12:

[Math Figure 12] cinit = i_ⁿs,NDi /²J+ *)· (^2Χ(η_ΧΙΟ,ΝΩΐ ) + l)' ²'⁶ + "SCID ^for one codeword scheduling cinit = (L"5/²J^{+ '} i^2Xn_SCID + !)· 2¹⁶ + ⁿsciD > ^{for two} codeword scheduling where n_SCID is dynamically determined by DCI between 0 and 1 such as an LTE Release 10 and NDI is a new data indicator of the disabled TB determined by DCI between 0 and 1. The parameter n_{s ND1} in Math Figure 12 is determined by Math Figure 13.

[Math Figure 13] ns ,NDI = ⁿs + ² NDi mod 20 where n_s is a slot number of a serving (or primary) cell of a UE, and A_NDI is a sub-frame offset value depending on an NDI in a range of size 10 such as [0, 9] or [-4, 5]. Note that the parameter of the slot number in the DMRS scrambling for two codewords scheduling is only dependent on the slot number of the serving (or primary) cell of the UE. The parameters x„_saD and ^x(_nsaD,NDi) is determined by Table 9 where XI, X2, X3, X4, X5 and X6 are signaled by higher layer and there can be a dependency among the six values in Table 9 such that X_(nsciDfi) = ^xn_saD mandating X1=X5 and X3=X6. One way to determine parameters, n_s<NDI , is to use Table 1 1 where Dl and D2 are signaled by higher layer.

[Table 11 ]

Another way to determine parameters n_s>ND1 is determined as follows:

. If x„_scm = Nf ^~' , UE uses the slot number of Cell-/.

. If x„_scjD≠Nf⁽ *"-ⁱ for all , a slot number is set to a default value (e.g.,

»s,NDI ⁼0)·

where

are the Cell-IDs of the cells Cell-1, Cell-2, Cell-M for which the UE reported RSRP at least once, or the Cell-IDs in the list of physical Cell-IDs which is signaled by an eNB. Note that the parameter of the slot number in the DMRS scrambling for two codewords scheduling is only dependent on that of the serving (or primary) cell of the UE.

For Tables 8, 9, 10 and 1 1, more indication states can be used if we add one bit n_SCID2 in order to indicate DMRS scrambling such as Tables 5 and 6.

In the CoMP scheme, a network can decide to transmit a PDSCH signal to a UE using different TPs which could belong to different cells having different Cell-IDs and slot numbers. Especially for a Dynamic cell Selection (DS) scheme and a Joint Transmission (JT) scheme, a TP transmitting a PDSCH signal for a CoMP UE is dynamically changed. Here, the CoMP UE is a UE supporting the CoMP scheme. Additionally, each cell can have different CRS start position since CRS starting position is determined by a preset equation, e.g., (Cell-ID mod 6).

FIG. 11 schematically illustrates RB structures for Cell-1 and Cell-2 which have different CRS starting positions in an LTE-A mobile communication system.

Referring to FIG. 1 1, if a CoMP UE between a Cell-1 and a Cell-2 receives a PDSCH signal from the Cell-1, CRS positions for the Cell-1 cannot be used for a PDSCH signal transmission while CRS positions for the Cell-2 cannot be used for the PDSCH transmission when the CoMP UE receives the PDSCH signal from the Cell-2. The CRS resource is a resource through a CRS is transmitted. Furthermore, when the CoMP UE receives the PDSCH signal from both the Cell-1 and the Cell-2 with a JT scheme, then both CRS positions of the Cell-1 and the Cell-2 cannot be used for the PDSCH transmission such as FIG. 12.

FIG. 12 schematically illustrates a RB structure if a JT scheme is used between a Cell-1 and a Cell-2 in an LTE-A mobile communication system.

Referring to FIG. 12, if a CoMP UE receives a PDSCH signal from the Cell-1 and the Cell-2 using the JT scheme, CRS resources from both the Cell-1 and the Cell-2 may not be used for a PDSCH signal transmission. That is, for CoMP UEs among multiple cells, there is a problem that REs available for a PDSCH signal transmission is dependent on which cell is transmitting PDSCH.

In an LTE Release 10, each cell has its own MBSFN (multimedia broadcast multicast service single frequency network) sub-frame configuration which is signaled with SystemInformationBlockType2 that includes cell-specific Radio Resource Control (RRC) information. Note that the MBSFN sub-frame used for a PDSCH signal transmission does not transmit a CRS in a PDSCH region.

FIG. 13 schematically illustrates a sub-frame structure in a case where 2 cells use different MBSFN sub-frame configurations in an LTE-A mobile communication system.

In FIG. 13, an MBSFN sub-frame which does not include a CRS resource is shown as "MBSFN", and a normal sub-frame including the CRS resource is shown as "Normal".

Referring to FIG. 13, a Cell-1 and a Cell-2 have different MBSFN sub- frame configurations. When a CoMP UE between the Cell-1 and the Cell-2 receives a PDSCH signal from the Cell-1 in sub-frame #1, CRS positions of the Cell-1 cannot be used for the PDSCH signal transmission while CRS resources do not need to be considered when the UE receives the PDSCH signal from the Cell-2 in sub-frame #2. In conclusion, for CoMP UEs among multiple cells, there is a problem that REs available for a PDSCH signal transmission is dependent on which cell and sub-frame is used for transmitting a PDSCH signal. In one alternative, an eNB transmits a RRC signal to indicate UE's PDSCH RE mapping. In order for a UE to determine PDSCH RE mapping for another cell than the serving cell, the eNB should signal to the UE a RRC signal including at least one of the following parameters for the cell:

. Physical Cell-ID (or Cell-ID mod 6)

. MBSFN sub-frame configuration

. Number of CRS port

. Sub-frame offset value from the reference (serving/primary) cell . Number of OFDM symbols to assume for control region

If the UE is configured with the above RRC signal for at least one cell, the UE would assume the PDSCH RE mapping for a cell using the JT scheme among the serving cell and all the cells related to the RRC signal. In the below, aforementioned the serving cell and all the cells regarding on the above RRC signal may be referred as "configured cells for CoMP" or a "CoMP cell". Here, the assumption of the PDSCH RE mapping for the cell using the JT scheme among all the CoMP cells implies that the UE does not expect a PDSCH signal transmission in all CRS REs for remaining CoMP cells excepting cells in which the scheduled sub-frame is configured as a MBSFN sub-frame. There are two ways for a UE to decode a PDSCH signal under the assumption of the PDSCH RE mapping for the cell using the JT scheme among all CoMP cells. The first way is rate-matching method where UEs decode a PDSCH signal under the assumption that an eNB maps data bits to REs in order of skipping CRS resources for all CoMP cells. On the other hand, the second way is puncturing method where UEs decode a PDSCH signal under the assumption that an eNB maps data bits to REs in order of the serving cell but punctures CRS resources for all CoMP cells.

FIG. 14 schematically illustrates a rate-matching scheme for a JT scheme in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention.

Referring to FIG. 14, a RE allocated as a CRS RE in a Cell-1 as a serving cell may be different from a RE allocated as a CRS RE in a Cell-2 different from the serving cell, so a UE receives a PDSCH signal only through REs which are- not the CRS RE allocated in the Cell-1 and the CRS RE allocated in the Cell-2, and a RE through the PDSCH signal is received is a PDSCH RE.

FIG. 15 schematically illustrates a puncturing scheme for a JT scheme in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention.

Referring to FIG. 15, a RE allocated as a CRS RE in a Cell-1 as a serving cell may be different from a RE allocated as a CRS RE in a Cell-2 different from the serving cell, so a UE punctures the CRS RE allocated in the Cell-1 and the CRS RE allocated in the Cell-2, receives a PDSCH signal only through REs except for the punctured CRS REs, and a RE through the PDSCH signal is received is a PDSCH RE.

In another alternative, eNB transmits one bit information dynamically indicating how a CoMP UE assumes the PDSCH RE mapping in DCI for PDSCH scheduling. If the one bit indicating the PDSCH RE mapping assumption is ON, the UE would assume the PDSCH RE mapping for the JT scheme among all configured cells for a CoMP scheme. That is, the assumption of the PDSCH RE mapping for the JT scheme among all the CoMP cells implies that the UE does not expect PDSCH transmission in all CRS REs for all CoMP cells excepting cells in which the scheduled sub-frame is configured as a MBSFN sub-frame. There are two ways for the UE to decode a PDSCH signal under the assumption of the PDSCH RE mapping for the JT scheme among all CoMP cells. The first way is a rate-matching scheme where UEs decode PDSCH under the assumption that eNB maps data bits to REs in order of skipping CRS REs for all CoMP cells as shown in FIG. 14. On the other hand, the second way is a puncturing scheme where UEs decode a PDSCH signal under the assumption that eNB maps data bits to REs in order of the serving cell but punctures CRS REs for all CoMP cells as shown in FIG. 15.

On the other hand, if the one bit indicating a PDSCH RE mapping assumption is OFF, the UE would assume the PDSCH RE mapping for the serving (primary) cell. In this case, the UE does not expect a PDSCH signal transmission in all CRS REs of the serving (primary) cell in which the scheduled sub-frame is not configured as a MBSFN sub-frame.

Table 12 shows the UE's assumption of the PDSCH RE mapping for the one bit information indicating PDSCH RE mapping. Note that in order for the UE to determine a PDSCH RE mapping for a cell, an eNB should signal at least one of the following parameters to the UE:

. Physical Cell-ID (or Cell-ID mod 6)

. MBSFN sub-frame configuration

. Number of CRS port

[Table 12]

In Table 12, a PDSCH RE mapping indication is expressed.

In other alternative, an eNB transmits one bit information dynamically indicating how a CoMP UE assumes the PDSCH RE mapping in DCI for a PDSCH scheduling. If the one bit for PDSCH RE mapping is ON, the UE would assume the PDSCH RE mapping for the JT scheme among a set of cells configured by higher layer signaling. More clearly, the assumption of the PDSCH RE mapping for the JT scheme among a set of cells configured by higher layer signaling implies that the UE does not expect PDSCH transmission in all CRS REs for all configured cells excepting cells in which the scheduled sub-frame is configured as a MBSFN sub-frame. Note that the configuration of the cells for the case that the one bit for PDSCH RE mapping is ON would be signaled by higher layer in UE specific manner.

On the other hand, if the one bit for PDSCH RE mapping is OFF, the UE would assume the PDSCH RE mapping for the serving (primary) cell. In this case, the UE does not expect a PDSCH signal transmission in all CRS REs of the serving (primary) cell in which the scheduled sub-frame is not configured as a MBSFN sub-frame. There are two ways for a UE to decode a PDSCH signal under the assumption of the PDSCH RE mapping for the JT scheme among multiple cells. The first way is rate-matching method where UEs decode a PDSCH signal under the assumption that eNB maps data bits to REs in order of skipping CRS resources for multiple cells for JT as shown in FIG. 14. On the other hand, the second way is puncturing method where UEs decode a PDSCH signal under the assumption that eNB maps data bits to REs in order of the serving cell but punctures CRS positions for multiple cells for a JT scheme as shown in FIG. 15.

Table 13 shows the UE's assumption of the PDSCH RE mapping for the one bit information indicating PDSCH RE mapping. Note that in order for UE to determine PDSCH RE mapping for a cell, eNB should signal at least one of the following parameters to the UE:

. Physical Cell-ID (or Cell-ID mod 6)

. MBSFN sub-frame configuration

. Number of CRS port

[Table 13 ]

Indication bit for UE's assumption of PDSCH RE

PDSCH RE mapping mapping 0 PDSCH RE mapping for the serving cell

PDSCH RE mapping for the JT among a

1 set of cells configured by higher layer signaling

In Table 13, a PDSCH RE mapping indication is expressed.

In other alternative, the indication of PDSCH RE mapping is tied to the DMRS scrambling indication. The reason for the joint indication between a DMRS scrambling and a PDSCH RE mapping is that determination of both DMRS scrambling and PDSCH RE mapping is related to which TP is used for a PDSCH transmission. For one example, the indication of the PDSCH RE mapping can be tied to Table 2 or Table 3 such as Table 14 or Table 15, respectively, where C, represents a cell and RE_mapping(C₁, C₂, C*) denotes the PDSCH RE mapping for the JT scheme among cells Ci, C₂, ..., C^ with κ≥ l . If K = l , RE mapping(Ci) denotes the PDSCH RE mapping for the cells Ci

There are two ways for a UE to decode a PDSCH signal under the assumption of the PDSCH RE mapping for the JT scheme among multiple cells. The first way is a rate-matching scheme where UEs decode a PDSCH signal under the assumption that an eNB maps data bits to REs in order of skipping CRS REs for multiple cells for the JT scheme as shown in FIG. 14. On the other hand, the second way is a puncturing scheme where UEs decode a PDSCH signal under the assumption that eNB maps data bits to REs in order of the serving cell but punctures CRS REs for multiple cells for the JT scheme as shown in FIG. 15.

Note that in order for the UE to determine a PDSCH RE mapping for a cell Ci, the eNB should signal at least one of the following parameters to the UE:

. Physical Cell-ID of C, (or Cell-ID mod 6)

. MBSFN sub-frame configuration information of C,

Number of CRS port of C,

Sub-frame offset value of C, from the reference (serving/primary) cell . Number of OFDM symbols to assume for control region

That is, if Table 14 is used, after two sets of (Dl, XI, RE_mapping(Ci, C₂, · · ·, C_K)) and (D2, X2, RE_mapping(C^₊₁, C_A:₊₂, C_K+L)) are configured to the UE by higher layer signaling, the UE may use n_sclD derived in DCI to determine one of the above two sets in one sub-frame scheduled for PDSCH transmission.

On the other hand, if Table 15 is used, after two pairs of (XI, RE_mapping(C,, C₂, C^)) and (X2, RE_mapping(C^₊₁, C_K+2, C_K+L)) are configured to the UE by higher layer signaling, the UE will use n_SCID derived in DCI to determine one of the two pairs in one sub-frame scheduled for a PDSCH signal transmission. As an alternative scheme, the last columns in Table 14 and Table 15 can include a fixed PDSCH RE mapping method without RRC signaling for the last columns such that " n_saD = 0" indicates PDSCH RE mapping for the serving cell and " n_SCID = 1" indicates PDSCH RE mapping for the neighboring cell, or vise versa.

[Table 14]

In Table 14, x_nscm , A„_SCID , and PDSCH RE mapping for «. ( K > l , L≥ l ) are expressed.

[ Table 15]

In Table 15, X„_SCID and PDSCH RE mapping for n_sclD , ( K≥\ , L≥I ) are expressed.

In an LTE Release 10, n_SCID is switched between 0 and 1 only for the case that the UE is scheduled with a PDSCH signal transmission of 1 layer or 2 layers. If the UE is configured with a PDSCH signal transmission of more than 2 layers, n_SCID is fixed to 0. Accordingly, if we just follow Table 14 or 15, PDSCH RE mapping cannot be switched between two candidates when the UE is scheduled with a PDSCH signal transmission of more than 2 layers.

Therefore, we can adopt additional feature to facilitate a PDSCH RE mapping for supporting a DS scheme and a JT scheme in a PDSCH signal transmission of more than 2 layers such as Table 16.

[Table 16]

In Table 16, a PDSCH RE mapping for the scheduled number of layers is expressed.

For Table 16, if a UE is configured with PDSCH transmission of 1 or 2 layers, the UE may assume the PDSCH RE mapping in Table 14 (or Table 15) which is dependent on the value of n_SCID . On the other hand, if the UE is configured with PDSCH transmission of more than 2 layers, the UE would assume the PDSCH RE mapping for the JT scheme among all CoMP cells. As another alternative to Table 16, the entry in the second row and the second column can be replaced to PDSCH RE mapping for the JT scheme among a set of cells configured by higher layer signaling such as Table 17. In this case, additional RRC signaling to indicate PDSCH RE mapping of more than 2 layers should be introduced.

Although, in Table 16 and Table 17, a PDSCH RE mapping is determined by whether the number of layers of PDSCH transmission is "1 or 2" or "more than 2", we do not restrict our invention to this case. That is, the switching point of a PDSCH RE mapping can be an arbitrary number of layers. For example, the PDSCH RE mapping can be determined by whether the number of layers of PDSCH transmission is "1" or "more than 1". The design assumption on this example is that PDSCH transmission of larger than one layer for CoMP UEs can occur only when the JT scheme is applied.

[Table 17] # of layers PDSCH RE mapping

1 or 2 use Table 14 (or Table 15)

PDSCH RE mapping for JT scheme among a set of cells

More than 2

configured by higher layer

signaling

In Table 17, a PDSCH RE mapping for the scheduled number of layers is expressed.

In an LTE mobile communication system, the system information and the paging information is transmitted to all UE in a cell regardless of UE capability. That is, system information and paging information is transmitted to Release 8/9/10 UEs as well as Release 1 1 UEs. Therefore, a PDSCH RE mapping for paging information and system information should use a PDSCH RE mapping identical to a PDSCH RE mapping of the serving cell.

When the UE is scheduled with the system information or the paging information, a PDCCH for the scheduling uses CRC (cyclic redundancy check) of a System Information-Radio Network Temporary Identifier (SI-RNTI) or a Paging-Radio Network Temporary Identifier (P-RNTI), respectively. Therefore, when the UE detects a PDCCH signal using the P-RNTI or the SI-RNTI, the UE just uses the PDSCH RE mapping of the serving cell. On the other hand, when the UE detects the PDCCH signal using other RNTI than the P-RNTI and the SI- RNTI, it would follow at least one of the new PDSCH RE mappings described in the above including methods described in Table 16 or 17.

FIG. 16 is a flowchart illustrating an example of a method for receiving a PDSCH signal in a UE in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention.

Referring to FIG. 16, a UE receives a PDCCH signal for a PDSCH scheduling in step 1611. The UE determines whether an SI-RNTI or a P-RNTI has been used for the PDCCH signal in step 1613. If the SI-RNTI and the P- RNTI have not been used for the PDCCH signal, the UE selects a new PDSCH RE mapping in which Table 16 or Table 17 is used in step 1615.

If the SI-RNTI or the P-RNTI has been used for the PDCCH signal, the UE selects a legacy PDSCH RE mapping for a serving cell in step 1617. The UE receives a PDSCH signal based on the selected PDSCH RE mapping in step 1619.

In a CoMP transmission mode (corresponding to transmission mode 9 in an LTE Release 10), UEs can be scheduled by one of the following combinations of DCI format and RNTI in a PDCCH (or an ePDCCH):

. DCI format 2C and Cell-Radio Network Temporary Identifier (C-

RNTI)

. DCI format 2C and Semi-Persistent Scheduling Cell-Radio Network Temporary Identifier (SPS C-RNTI)

. DCI format 1A and C-RNTI

. DCI format 1A and SPS C-RNTI

. DCI format 1 A and P-RNTI

. DCI format 1A and SI-RNTI

. DCI format 1A and Random Access Radio Network Temporary Identifier (RA-RNTI)

. DCI format 1 C and P-RNTI

. DCI format 1C and SI-RNTI

. DCI format 1C and RA-RNTI

For the above combinations, the DCI format 2C is used for PDSCH scheduling with up to 8-layer transmission based on DMRS and includes indication fields to realize possible dynamic CoMP operations. DCI format 1A is used for a compact PDSCH scheduling with a small indication field. The DCI format 1C is used for a very compact PDSCH scheduling and dedicated to scheduling for paging, system information, or random access procedure. Additionally, the C-RNTI is used for a data scheduling and the SPS C-RNTI is used for a semi-persistent scheduling of data. The P-RNTI, SI-RNTI, and RA- RNTI are for scheduling of paging, system information, and random access messages, respectively.

For a UE, data is dedicated to that UE such that is can be transmitted by using a DS scheme or a JT scheme, while paging and system information are broadcast information to multiple UEs including LTE Release 8/9/10 UEs as well as LTE Release 11 UEs. Random access messages are used for various cases including lost of synchronization for the UE. Based on the discussion on the use of DCI formats and RNTIs, UE assumption on a PDSCH RE mapping for each combination of DCI format and RNTI in the CoMP transmission mode can be defined as Table 18.

In Table 18, New RE mapping for CoMP means at least one of the above mentioned PDSCH RE mapping alternatives for a CoMP scheme. Legacy RE mapping for the serving cell denotes PDSCH RE mapping method for each case defined in LTE Release 10 specification. If a UE assumption on PDSCH RE mapping in Table 18 is used, switching between the new RE mapping and the legacy RE mapping can be based on a RNTI. That is, if the C-RNTI or the SPS RNTI is used for scheduling of a CoMP UE, the new PDSCH RE mapping applies while the legacy PDSCH RE mapping is used if the P-RNTI, the SI- RNTI or the RA-RNTI is used for the scheduling.

FIG. 17 is a flowchart illustrating another example of a method for receiving a PDSCH signal in a UE in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention.

Referring to FIG. 17, a UE receives a PDCCH signal for a PDSCH scheduling in step 1711. The UE determines whether a C-RNTI or an SPS C- RNTI has been used for the PDCCH signal in step 1713. If the C-RNTI or the SPS C-RNTI has been used for the PDCCH signal, the UE selects a new PDSCH RE mapping in which Table 18 is used in step 1715.

If the C-RNTI and the SPS C-RNTI have not been used for the PDCCH signal, the UE selects a legacy PDSCH RE mapping for a serving cell in step 1717.

The UE receives a PDSCH signal based on the selected PDSCH RE mapping in step 1719.

In FIG. 17, note that the UE can decide a PDSCH RE mapping assumption of the UE between a new RE mapping and a legacy RE mapping after the UE detects both of the DCI format and the RNTI. The decision may be based on Table 18.

[Table 18]

Combination of DCI format

PDSCH RE mapping

and RNTI

DCI format 2C and C-RNTI New RE mapping for CoMP

DCI format 2C and SPS C- New RE mapping for CoMP RNTI

DCI format 1A and C-RNTI New RE mapping for CoMP

DCI format 1A and SPS C-

New RE mapping for CoMP

RNTI

Legacy RE mapping for the

DCI format 1 A and P-RNTI

serving cell

Legacy RE mapping for the

DCI format 1A and SI-RNTI

serving cell

Legacy RE mapping for the

DCI format 1 A and RA-RNTI

serving cell

Legacy RE mapping for the

DCI format 1C and P-RNTI

serving cell

Legacy RE mapping for the

DCI format 1C and SI-RNTI

serving cell

Legacy RE mapping for the

DCI format 1C and RA-RNTI

serving cell

In Table 18, a UE assumption on a PDSCH RE mapping is expressed.

Since DCI format 1A includes a small indication field, it could not be appropriate to a CoMP scheduling. For this reason, data transmission of scheduling by DCI format 1A might not go with a DS scheme or a JT scheme. Based on this situation for the DCI format 1A, UE assumption on a PDSCH RE mapping for each combination of a DCI format and a RNTI in the CoMP transmission mode can be defined as Table 19.

If a UE assumption on a PDSCH RE mapping in Table 19 is used, switching between a new RE mapping and a legacy RE mapping can be based on a DCI format. That is, if the DCI format 2C is used for scheduling of a CoMP UE, the new PDSCH RE mapping applies while the legacy PDSCH RE mapping is used if the DCI format 1A or the DCI format 1C is used for the scheduling.

FIG. 18 is a flowchart illustrating still another method for receiving a PDSCH signal in a UE in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention.

Referring to FIG. 18, a UE receives a PDCCH signal for a PDSCH scheduling in step 181 1. The UE determines whether a DCI format 2C has been used for the PDCCH signal in step 1813. If the DCI format 2C has been used for the PDCCH signal, the UE selects a new PDSCH RE mapping in which Table 19 is used in step 1815.

If the DCI format 2C has not been used for the PDCCH signal, the UE selects a legacy PDSCH RE mapping for a serving cell in step 1817.

The UE receives a PDSCH signal based on the selected PDSCH RE mapping in step 1819.

In FIG. 18, Note that the UE can decide a PDSCH RE mapping assumption of the UE between a new RE mapping and a legacy RE mapping after the UE detects both of the DCI format and the RNTI. The decision may be based on Table 19.

[Table 19]

Combination of DCI format

PDSCH RE mapping

and RNTI

DCI format 2C and C-RNTI New RE mapping for CoMP

DCI format 2C and SPS C-

New RE mapping for CoMP

RNTI

Legacy RE mapping for the

DCI format 1A and C-RNTI

serving cell

DCI format 1A and SPS C- Legacy RE mapping for the

RNTI serving cell

Legacy RE mapping for the

DCI format 1 A and P-RNTI

serving cell

Legacy RE mapping for the

DCI format 1A and SI-RNTI

serving cell

Legacy RE mapping for the

DCI format 1 A and RA-RNTI

serving cell

Legacy RE mapping for the

DCI format 1C and P-RNTI

serving cell

Legacy RE mapping for the

DCI format 1C and SI-RNTI

serving cell

Legacy RE mapping for the

DCI format 1C and RA-RNTI

serving cell | In Table 19, a UE assumption on a PDSCH RE mapping is expressed.

For another example, the indication of the PDSCH RE mapping can be tied to Table 20 or Table 21 such as Table 4 or Table 5, respectively, where C, represents a cell and RE_mapping(C₁, C₂, C_K) denotes the PDSCH RE mapping for the JT scheme among cells Q, C₂, C_K with κ≥ι . If κ = ι , RE_mapping(C₁) denotes the PDSCH RE mapping for the cells C_}. Note that in order for the UE to determine the PDSCH RE mapping for a cell C„ an eNB should signal at least one of the following parameters to the UE:

. Physical Cell-ID of Q (or Cell-ID mod 6)

. MBSFN sub-frame configuration of C,

. Number of CRS port of C,

. Sub-frame offset value of C, from the reference (serving/primary) cell . Number of OFDM symbols to assume for control region

That is, if Table 20 is used, after two sets of (Dl, XI, RE mapping^, C₂, C )) and (D2, X2, RE mapping^^, C_K+2, C_K+L)) are configured to the UE by higher layer signaling, the UE may use n_saD2 derived in DCI to determine one of the two sets in one sub-frame scheduled for PDSCH transmission. On the other hand, if Table 21 is used, after two pairs of (XI, RE_mapping(C C₂, C*)) and (X2, RE_mapping(C^₊₁, C_K+2, C_K+L)) are configured to the UE by higher layer signaling, the UE may use n_sclD2 derived in DCI to determine one of the two pairs in one sub-frame scheduled for PDSCH transmission.

[Table 20]

In Table 20, x„_sao2 , A„_scm2 , and a PDSCH RE mapping for „_; ( K≥ l , L≥ l ) are expressed.

[Table 21 ] ⁿSClD2 PDSCH PvE mapping

0 XI RE_mapping(C_b C₂, C_K)

1 X2 RE_mapping(C^₊₁, C_K+2, C_K+L)

In Table 21, x_nscim and a PDSCH RE mapping for n_sclD2 , ( K≥I , L≥I ) are expressed.

In other alternative, the indication of PDSCH RE mapping is not only dependent on the DMRS scrambling but also additional one bit information dynamically indicating whether a CoMP UE assumes the PDSCH RE mapping for the JT among all configured cells for CoMP or not. That is, if the additional one bit for PDSCH RE mapping is ON, the UE would assume the PDSCH RE mapping for the JT among all configured cells for CoMP. On the other hand, if the additional one bit for PDSCH RE mapping is OFF, the UE would assume the PDSCH RE mapping which is described in Table 14, 15, 20, 21 , 22, or 23. For example of Table 14, after two sets of (Dl, XI, RE_mapping(C₁, C₂, C^)) and (D2, X2, RE_mapping(C_/i;₊₁, C^₊₂, C_K+L)) are configured to a UE by higher layer signaling, the UE may use n_saD derived in DCI to determine one of the two sets in one sub-frame scheduled for PDSCH transmission if the one bit for PDSCH RE mapping is OFF. On the other hand, if the one bit for a PDSCH RE mapping is ON, the UE would determine x„_sao , A_nsciD by using n_SCID , while

PDSCH RE mapping for the JT among all configured cells for a CoMP scheme is assumed.

Note that in the above alternatives, cells in the network would share their physical Cell-IDs and/or virtual cell-IDs in use such as XI, X2, X3, X4 in order to coordinate inter- TP interference among multiple TPs in the networks.

FIG. 19 schematically illustrates an internal structure of a UE in a cellular radio communication system using a CoMP scheme according to an embodiment of the present invention.

Referring to FIG. 19, a UE includes a receiver 1911, a controller 1913, a transmitter 1915, and a storage unit 1917.

The controller 1913 controls the overall operation of the UE, specially controls the UE to perform an operation of receiving a DMRS and a PDSCH signal, i.e., an operation related to a DMRS scrambling and a PDSCH RE mapping according to an embodiment of the present invention. The operation of receiving the DMRS and the PDSCH signal is performed in the manner described before with reference to FIGs. 9 to 18, so the detailed description will be omitted herein.

The receiver 1911 receives signals from a Node B under a control of the controller 1913. The signals received in the receiver 1911 are described before with reference to FIGs. 9 to 18, so the detailed description will be omitted herein.

The transmitter 1915 transmits signals to the Node B under a control of the controller 1913. The signals transmitted in the transmitter 1915 are described before with reference to FIGs. 9 to 18, so the detailed description will be omitted herein.

The storage unit 1917 stores the signals received by the receiver 1911 and data for an operation of the UE, e.g., information related to the operation of receiving the DMRS and the PDSCH signal.

While the receiver 1911, the controller 1913, the transmitter 1915, and the storage unit 1917 are shown in FIG. 19 as separate units, it is to be understood that this is for merely convenience of description. In other words, the receiver 1911, the controller 1913, the transmitter 1915, and the storage unit 1917 may be incorporated into a single unit.

Referring to FIG. 20, a Node B includes a receiver 2011, a controller 2013, a transmitter 2015, and a storage unit 2017.

The controller 2013 controls the overall operation of the Node B, specially controls the Node B to perform an operation related to a DMRS reception operation and a PDSCH signal reception operation, i.e., a DMRS scrambling and a PDSCH RE mapping in a UE according to an embodiment of the present invention. The operation related to the DMRS reception operation and the PDSCH signal reception operation in the UE is performed in the manner described before with reference to FIGs. 9 to 18, so the detailed description will be omitted herein.

The receiver 2011 receives signals from the UE, a Node B, etc under a control of the controller 2013. The signals received in the receiver 2011 are described before with reference to FIGs. 9 to 18, so the detailed description will be omitted herein. The transmitter 2015 transmits signals to the UE, the Node B, etc under a control of the controller 2013. The signals transmitted in the transmitter 2015 are described before with reference to FIGs. 9 to 18, so the detailed description will be omitted herein.

The storage unit 2017 stores the signals received by the receiver 2011 and data for an operation of the Node B, e.g., information related to the DMRS reception operation and the PDSCH signal reception operation in the UE.

While the receiver 2011, the controller 2013, the transmitter 2015, and the storage unit 2017 are shown in FIG. 20 as separate units, it is to be understood that this is for merely convenience of description. In other words, the receiver 2011, the controller 2013, the transmitter 2015, and the storage unit 2017 may be incorporated into a single unit.

While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. A method for transmitting a DeModulation Reference Signal (DMRS) by a Node B in a cellular radio communication system using a Cooperative Multi-Point (CoMP) scheme, comprising:

for at least one antenna port, transmitting a DMRS based on a preset DMRS scrambling sequence,

wherein the DMRS scrambling sequence is initialized with an initial value at a start of each sub- frame, and

wherein the initial value is determined using an identifier of the DMRS scrambling sequence, a slot number of a serving (or primary) cell of a related User Equipment (UE), a sub-frame offset value based on the DMRS scrambling sequence, and a parameter related to a cell identifier of a cell for which the related UE has reported a Reference Signal Received Power (RSRP) at least once.

2. The method as claimed in claim 1, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is different from the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a preset default value.

3. The method as claimed in claim 1, wherein the initial value is determined further using an additional parameter determined by Downlink Control Information (DCI) for a Physical Downlink Shared Channel (PDSCH) scheduling among integers in a preset range.

4. The method as claimed in claim 3, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is different from the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a preset default value.

5. The method as claimed in claim 1, wherein the initial value is determined further using a number of codewords scheduled for the related UE and a New Data Indicator (NDI) for a disabled transport block determined by Downlink Control Information (DCI).

6. The method as claimed in claim 5, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

7. The method as claimed in claim 5, wherein, when the number of codewords scheduled for the related UE is a preset number and a value of the NDI is a preset number,

if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is different from the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a preset default value.

8. A method for receiving a DeModulation Reference Signal (DMRS) by a User Equipment (UE) in a cellular radio communication system using a Cooperative Multi-Point (CoMP) scheme, comprising:

receiving a DMRS from a Node B,

wherein, for at least one antenna port, the DMRS is transmitted based on a preset DMRS scrambling sequence,

wherein the DMRS scrambling sequence is initialized with an initial value at a start of each sub-frame, and

wherein the initial value is determined using an identifier of the DMRS scrambling sequence, a slot number of a serving (or primary) cell of a related UE, a sub-frame offset value based on the DMRS scrambling sequence, and a parameter related to a cell identifier of a cell for which the related UE has reported a Reference Signal Received Power (RSRP) at least once.

9. The method as claimed in claim 8, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

10. The method as claimed in claim 8, wherein the initial value is determined further using an additional parameter determined by Downlink Control Information (DCI) for a Physical Downlink Shared Channel (PDSCH) scheduling among integers in a preset range.

11. The method as claimed in claim 10, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

12. The method as claimed in claim 8, wherein the initial value is determined further using a number of codewords scheduled for the related UE and a New Data Indicator (NDI) for a disabled transport block determined by Downlink Control Information (DCI).

13. The method as claimed in claim 12, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

14. The method as claimed in claim 12, wherein, when the number of codewords scheduled for the related UE is a preset number and a value of the NDI is a preset number,

15. A Node B in a cellular radio communication system using a Cooperative Multi-Point (CoMP) scheme, comprising:

a transmitter for transmitting a DeModulation Reference Signal (DMRS) based on a preset DMRS scrambling sequence, for at least one antenna port,

16. The Node B as claimed in claim 15, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

17. The Node B as claimed in claim 15, wherein the initial value is determined further using an additional parameter determined by Downlink Control Information (DCI) for a Physical Downlink Shared Channel (PDSCH) scheduling among integers in a preset range.

18. The Node B as claimed in claim 17, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

19. The Node B as claimed in claim 15, wherein the initial value is determined further using a number of codewords scheduled for the related UE and a New Data Indicator (NDI) for a disabled transport block determined by Downlink Control Information (DCI).

20. The Node B as claimed in claim 19, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

21. The Node B as claimed in claim 19, wherein, when the number of codewords scheduled for the related UE is a preset number and a value of the NDI is a preset number,

22. A User Equipment (UE) in a cellular radio communication system using a Cooperative Multi-Point (CoMP) scheme, comprising:

a receiver for receiving a DeModulation Reference Signal (DMRS) from a Node B,

23. The UE as claimed in claim 22, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

24. The UE as claimed in claim 22, wherein the initial value is determined further using an additional parameter determined by Downlink Control Information (DCI) for a Physical Downlink Shared Channel (PDSCH) scheduling among integers in a preset range.

25. The UE as claimed in claim 24, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

26. The UE as claimed in claim 22, wherein the initial value is determined further using a number of codewords scheduled for the related UE and a New Data Indicator (NDI) for a disabled transport block determined by Downlink Control Information (DCI).

27. The UE as claimed in claim 26, wherein, if the parameter related to the cell identifier of the cell for which the related UE has reported the RSRP at least once is identical to the cell identifier of the cell for which the related UE has reported the RSRP at least once, the slot number is set to a slot number of the cell for which the related UE has reported the RSRP at least once, and

28. The UE as claimed in claim 26, wherein, when the number of codewords scheduled for the related UE is a preset number and a value of the NDI is a preset number,